Just FWIW, don't get too bent out of shape around rank. In situations like this, rank doesn't represent much more than your experience and your pay. The chain of command is all that matters. NCOIC, OIC, and whatever team-leader positions come up -- those are the marks of authority, and 'sergeant' or 'corporal' is really just a detail. 

TLDR -- don't sweat rank in your character sheet, it's not a big deal in practice.